I have made a bat house and now I have put it up. To do so I purchased two teen foot galvanized steel poles at Home Depot, and attached them together. Where they meet I drilled a hole through the two and put a 4" bolt and wingnut through the hole to help hold the two together. At the bottom of I dug a 1.5 foot by 1 foot hole and put in 80 lbs bag of quickcrete, and then attached the bottom end of the pole that is about 2" from the ground to a raised bed that is about 2' tall, full of dirt, and attached it where the raised bed end and side meet with a 2×4 post that holds the two ends together of the bed. So I have the pole in concrete, and attached to the raised bed with two u brackets. End result is I have a cedar bat house attached to the very top about 17.5 feet off of the ground. The bat house weighs maybe 5 pounds? It's a 3 chambered bat house.
When the wind blows I see the top half of the pole sway a bit, but the bottom portion stays relatively straight without much wobble. It's not a huge wobble but it does sway a bit. I guess where I am going with this is seeking someone to tell me if they think this will be strong enough to hold the structure for the long haul, or if there is something else I need to do to further reinforce the two poles together. I would hate to have 30+ bats living in the house and then it fall or something.
My gut is saying "hey silly, you have this thing in a huge concrete hole, and attached to a 2' raised bed for extra support. Sure it's going to sway a bit where the two poles meet in the middle, since it isn't one solid pole, but it will be fine. Drink a beer or something." Other part of me just wants someone who is more experienced or has more hair on their chest to offer their thoughts or opinion.
Any advice or suggestions would be greatly appreciated.
Best Answer
My estimate from the information given so far is that the nearly 18 foot high pole is not adequately anchored just by embedding the end of it in smallish block of concrete and a couple of U-bolts into a plank at ground level. (The block and u-bolt locations are smallish when you consider the overall pole lever arm length).
This thing should have a set of three guy wires coming down from about the 13 or 14 foot level that come down at angles to the ground and are anchored to their own piers of concrete in the ground. The bottom end of the guys would want to be out 13 to 17 feet from the bottom of the pole and spaced radially around the pole at 120 degree spacing.
This procedure will ensure that a high force wind will not take down your bat house and crash it upon someone or some other property.